1. Field of the Invention
The present invention relates to a composition comprising release agent and particulate material, for application to one or both of the fuser member and the substrate in toner fusing systems and processes. The present invention further relates to combating toner marking, by means of applying the composition as indicated to one or both of the fuser member and the substrate in toner fusing systems and processes.
2. Description of Background and other Information
Generally in electrostatographic reproduction, the original to be copied is rendered in the form of a latent electrostatic image on a photosensitive member. This latent image is made visible by the application of electrically charged toner.
The toner thusly forming the image is transferred to a substratexe2x80x94also referred to as a receiverxe2x80x94such as paper or transparent film, and fixed or fused to the substrate. Where heat softenable tonersxe2x80x94for example, comprising thermoplastic polymeric bindersxe2x80x94are employed, the usual method of fixing toner to the substrate involves applying heat to the toner, once it is on the substrate surface, to soften it, and then allowing or causing the toner to cool. This application of heat in the fusing process is preferably at a temperature of about 90xc2x0 C.-220xc2x0 C.; pressure may be employed in conjunction with the heat.
A system or assembly for providing the requisite heat and pressure customarily includes a fuser member and a support member. The heat energy employed in the fusing process generally is transmitted to toner on the substrate by the fuser member. Specifically, the fuser member is heated; to transfer heat energy to toner situated on a surface of the substrate, the fuser member contacts this toner, and correspondingly also can contact this surface of the substrate itself. The support member contacts an opposing surface of the substrate.
Accordingly, the substrate can be situated or positioned between the fuser and support members, so that these members can act together on the substrate to provide the requisite pressure in the fusing process. In cooperating, preferably the fuser and support members define a nip, or contact arc, in which the substrate is positioned or resides, and/or through which the substrate passes. Also as a matter of preference, the fuser and support members are in the form of fuser and pressure rollers, respectively. Yet additionally as a matter of preference, one or both of the fuser and support members have a soft layer that increases the nip, to effect better transfer of heat to fuse the toner.
During the fusing process toner can be offset from the substrate to the fuser member. Toner thusly transferred to the fuser member in turn may be passed on to other members in the electrostatographic apparatus, or to subsequent substrates subjected to fusing.
Toner on the fusing member therefore can interfere with the operation of the electrostatographic apparatus and with the quality of the ultimate product of the electrostatographic process. This offset toner is accordingly regarded as contamination of the fuser member, and preventing or at least minimizing this contamination is a desirable objective.
Release agents can be applied to fusing members during the fusing process, to combat toner offset. These agents usually are or include polyorganosiloxanes, particularly polyorganosiloxane oils.
U.S. Pat. No. 5,781,840 states that wicking agents may be applied to fuser members to prevent toner offset, and teaches a wicking agent comprising an organopolysiloxane, and at least about 1xc2x710xe2x88x926 weight percent of a metal compound. The organopolysiloxane has Sixe2x80x94H functional groups, and the metal compound is effective for promoting reaction between the organopolysiloxane Sixe2x80x94H functional groups, and reactive sites on the fuser member surface.
The metal compound in the wicking agent may comprise a metal salt, and the salt may be complexed with an organic ligand. The fuser member may have a polymeric surface layer comprising inert particulate filler, such as metal oxides like aluminum and tin oxides.
Use of talcum powder as a release agent is also known. U.S. Pat. No. 4,000,957 discusses dispensing this powder either onto the toner and paper before it reaches the fuser roller, or onto the fuser roller itself. Application of talcum powder to the fuser roller is indicated to be either simultaneously with, or subsequent to, application of a liquid release material. Only separate application of talcum powder and liquid release material, each from its own dispenser, is disclosed.
As to the indicated application of powder to toner and paper, this patent teaches use of a dispensing mechanism suitable for dispensing approximately 0.25 milligrams of talcum powder per square centimeter of toner image. This rate of application for particulate material translates into over 4 kilograms of particulate material for every 10,000 copies.
Employment of particulate material at this high a rate is undesirable for high speed copier-printer applications. If particulate material applied at this rate were used in the form of dispersion in a liquid medium, such as a liquid release agent, viscosity would be unacceptably high.
This patent also teaches a preferred size of 0.1 to 10 microns for the talcum powder. Because of this particle size range and the distribution, the stability of the dispersion in carrier media would not be high; particulate accordingly would tend to accumulate in the dispensing mechanism, and affect flow rate.
Once the desired toner-formed image is fixed in its intended location on a substrate, it may be subjected to contact by other surfaces that will cause displacement from the intended location. This displacement may be in the form of smearing and/or transfer to the contacting surface, and can be referred to as toner marking.
For instance, in the case of the substrate being a single sheet, it may be subjected to folding, mailing, or reprinting (either the same side or the back side of the sheet). Where it is one of several or one of hundreds of sheets, the sheets may be processed further by operations including, for example, sorting, binding, insertion of other media, character recognition, and booklet making. Any of these or similar operations can cause the toner-formed image to contact other surfaces and leave an objectionable mark, caused by the relocation of toner from its original place of deposition and fixation. This marking can appear on a variety of locationsxe2x80x94e.g., the backside of another sheet, another portion of the same sheet (when folded), or some other surface that would be visible to the intended recipient of the material.
It is known that toner marking can be combated by a number of methods. Among these are including wax additives in the toner, increasing the toughness of the toner, adding release lubricants to the toner surface, and reducing the force of contact causing the toner marking.
In this regard, U.S. Pat. Nos. 4,165,308 and 4,167,602 disclose electrographic recording materials, and coating compositions therefor, to improve toner adhesion and reduce toner smear. U.S. Pat. No. 4,859,550 discloses polymeric alcohols and aliphatic hydrocarbons as additives against toner offsetting and image smearing. U.S. application Ser. No. 09/387,586, filed Aug. 31, 1999, discloses a fuser member having a silicone rubber fusing surface that incorporates a controlled particle size filler; this fuser member maintains a low surface roughness, which reduces the roughness of the fused toner image, thus reducing toner marking. U.S. Pat. No. 5,209,464 discloses a sheet feed apparatus with a scuff feeder device that minimizes high pressure points contributing to toner ruboff.
In modern operations, images may be processed at a later time on unrelated equipment. Accordingly, sheets bearing these images should be able to minimize marking in a variety of paper handling equipment.
As indicated, application of release agents can be employed as a measure against toner offset. These materials, usually in the form of polydimethylsiloxane oils, also are known to reduce toner marking for a brief period after application. And in fact, as compared with other means of combating toner marking in an electrostatographic system, the use of a release agent has the advantage of minimizing impact on other subsystems, because fusing is one of the last steps in electrostatographic processes. However, the oil is absorbed into the substrate relatively quickly, and therefore as a practical matter is ineffective for use in combating toner marking.
In the field of offset printing, contamination caused by the ink used to form the intended images is also a factor to be addressed. For instance, this type of contamination can interfere with a process where an offset printer is applying ink to a succession of sheets that are thereafter stacked. If the ink is still wet when the sheets exit the printing stage, then during stacking ink can be transferred from sheet to sheet.
One means for combating this contamination is by dusting the image side of the sheets, with a material such as corn starch, after they leave the printing stage and prior to their stacking. As the sheets go into the stacker, they pass underneath an air blower apparatus that performs the dusting, so that the thusly applied material lies between the stacked sheets.
However, this dusting procedure itself leads to possible problems, such as contamination of machinery by the dusted material. And particularly, this material can be a health hazard.
In this regard, the material used for dusting can become airborne, and take a long time to settle out. Particles which have a diameter larger than about 2.5 microns are blocked in the nasal passages, and do not reach the lungs, while particles smaller than about 0.5 microns have sufficient Brownian motion, so that they do not stick to the inside wall of the lungs, and are breathed out.
However, particles of about 0.5 microns to about 2.5 microns are small enough to reach the lungs, and will stay there when breathed in. Of the material used for dusting, it is the particles in this size range that present the health hazard.
It has been discovered that a carrier medium may be used for impartingxe2x80x94to the substrate surface, and particularly to toner residing thereonxe2x80x94an agent for acting against, or combatingxe2x80x94e.g., preventing or prohibiting, or at least inhibiting, or lessening, or reducingxe2x80x94toner marking. In this regard, the invention pertains to a composition for combating toner marking. This composition can be referred to as a treating composition.
The treating composition is for application to toner residing on a substrate surface. It comprises particulate material and at least one carrier medium. Preferably, the particulate material is for combating contact between the toner and other surfaces. With the particulate material incorporated in the carrier medium, this material does not present the potential contamination or health hazard problems of the indicated dusting employed in offset printing.
The invention further pertains to a process for fusing toner, residing on a substrate surface, to the substrate surface. This process utilizes the treating composition as indicated, with the carrier medium comprising at least one release agent. The process comprises applying the treating composition to the surface of a fuser member, and contacting the toner with the fuser member surface bearing this composition.
The invention yet additionally pertains to a process for combating toner marking. This process comprises applying the treating composition, to the surface of toner previously fused to a substrate surface.
Preferably the particulate material of the treating composition comprises, or consists essentially of or consists substantially of, particles that are spherical, or at least near spherical, or at least essentially spherical or at least substantially spherical, in shape. Also as a matter of preference, the particulate material comprises, or consists essentially of or consists substantially of, particles that are uniform, or at least nearly uniform, or at least essentially uniform or at least substantially uniform, in size.